Minimum orbit intersection distance (original) (raw)

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Measure of close approach or collision risk in astronomy

The orbit of (4953) 1990 MU, which, with a MOID of 0.0263 AU, is classified as a potentially hazardous object

Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects.[1][2] It is defined as the distance between the closest points of the osculating orbits of two bodies. Of greatest interest is the risk of a collision with Earth. Earth MOID is often listed on comet and asteroid databases such as the JPL Small-Body Database. MOID values are also defined with respect to other bodies as well: Jupiter MOID, Venus MOID and so on.

An object is classified as a potentially hazardous object (PHO) – that is, posing a possible risk to Earth – if, among other conditions, its Earth MOID is less than 0.05 AU. For more massive bodies than Earth, there is a potentially notable close approach with a larger MOID; for instance, Jupiter MOIDs less than 1 AU are considered noteworthy since Jupiter is the most massive planet.[1]

A low MOID does not mean that a collision is inevitable as the planets frequently perturb the orbit of small bodies. It is also necessary that the two bodies reach that point in their orbits at the same time before the smaller body is perturbed into a different orbit with a different MOID value. Two objects gravitationally locked in orbital resonance may never approach one another. Numerical integrations become increasingly divergent as trajectories are projected further forward in time, especially beyond times where the smaller body is repeatedly perturbed by other planets. MOID has the convenience that it is obtained directly from the orbital elements of the body and no numerical integration into the future is used.[3]

The only object that has ever been rated at 4 on the Torino Scale (since downgraded), the Aten asteroid (99942) Apophis, has an Earth MOID of 0.00026 AU (39,000 km; 24,000 mi). This is not the smallest Earth MOID in the catalogues; many bodies with a small Earth MOID are not classed as PHO's because the objects are less than roughly 140 meters in diameter (or absolute magnitude, H > 22). Earth MOID values are generally more practical for asteroids less than 140 meters in diameter as those asteroids are very dim and often have a short observation arc with a poorly determined orbit. As of September 2023, there have been seven objects detected and their Earth-MOID calculated before the Earth impact.[4] The first two objects that were detected and had their Earth-MOID calculated before Earth impact were the small asteroids 2008 TC3 and 2014 AA. 2014 AA is listed with a MOID of 0.00000045 AU (67 km; 42 mi),[5] and is the second smallest MOID calculated for an Apollo asteroid after 2020 QY2 with an Earth-MOID of 0.00000039 AU (58 km; 36 mi).[6]

Potentially hazardous asteroids with Earth MOID < 0.0004 AU (~60,000km or ~5 Earth diameters) include:[7]

Numbered periodic comets with Earth MOID < 0.02 AU (~3 million km) include:

Some well known Main-belt asteroidswith Earth MOID < 1 AU

• Asteroid impact prediction
• List of Mercury-crossing minor planets
• List of Venus-crossing minor planets
• List of Earth-crossing minor planets
• List of Mars-crossing minor planets
• List of Jupiter-crossing minor planets
• List of Saturn-crossing minor planets
• List of Uranus-crossing minor planets
• List of Neptune-crossing minor planets

1. ^ a b Bruce Koehn, "Minimum Orbital Intersection Distance", Lowell Observatory, retrieved online 14 May 2009, archived 15 July 2015.
2. ^ Basics of Space Flight: The Solar System, p. 3, NASA Science, retrieved 14 May 2009 (from JPL site), archived 17 September 2021.
3. ^ Brian G. Marsden, "Press Information Sheet:Potentially Hazardous Asteroids", Harvard-Smithsonian Center for Astrophysics, retrieved online 3 May 2009, archived 22 November 2009.
4. ^ List of Prior Impacts, NEODyS, retrieved 23 September 2023.
5. ^ JPL SBDB: 2014 AA (Earth impactor on 1 January 2014)
6. ^ JPL SBDB: 2020 QY2 (Near-Earth asteroid roughly 2–meters in diameter)
7. ^ "JPL Small-Body Database Search Engine: Group: PHA and Orbit Constraint: Earth MOID < 0.0004 (AU)" (currently defined at an epoch of 2023-Sep-13). JPL Solar System Dynamics. Retrieved 20 September 2023.
8. ^ "JPL Small-Body Database: (2016 FG60)" (last observation: 2020-06-17; arc: 4.29 years). Jet Propulsion Laboratory. Archived from the original on 28 May 2019. Retrieved 23 September 2023.
9. ^ JPL SBDB: 73P-BW (Short-lived comet fragment)

• Fast Geometric Method for Calculating Accurate Minimum Orbit Intersection Distances (PDF)
• MOID for all NEOs (Near-Earth Objects) for Mercury to Jupiter (Updated Daily)
• List of the Potentially Hazardous Asteroids (PHAs)
• MBPL - Minor Body Priority List ( PHA Asteroids )
• SAEL - Small Asteroids Encounters List